March 1, J 91 7.] 



THE INDIA RUBBER WORLD 



317 



The Nature and Uses of Rubber Solvents — I. 



By Lothar E. Weber. Ph.D. 



Un thesecond installment of this article Dr. Weber will discuss benzol, solvent naphtha, shale oil, carbon bisulphide and carbon 



tetrachloride.] 



IT is only in one or two specialized branches of the rubber 

 industry that solvents play an integral part in the process 

 of manufacture. On the other hand, the large majority of 

 rubber articles require the services of a solvent in some part 

 of their manufacture, or at least for some component part enter- 

 ing into their manufacture. The function of the solvent in the 

 latter case may seem to be an unimportant one, but the manu- 

 facturer would be sorely pressed without its aid. The im- 

 portance of the solvent is realized more vividly when for any 

 one of a number of reasons it becomes a source of defective 

 goods. It can be said that just as a chain is no stronger than 

 its weakest link, so is a rubber article no stronger than its 

 cement. Accordingly, the question of solvents is an important 

 one for the rubber industry and the rubber manufacturer. 



While the number of liquids which have the property of dis- 

 solving rubber is numerous, relatively few of them find com- 

 mercial application in rubber manufacture. The origin of these 

 latter it is proposed briefly to describe, as well as their use in 

 the rubber industry, the specifications which they should meet, 

 and the defects caused by failure to meet these specifications. 



GASOLENE. 



In this country the solvent which finds the most extensive ap- 

 plication in the rubber industry is gasolene. This material is a 

 product of crude petroleum, in which it is present to the extent 

 of from 10 to 15 per cent, depending on the origin of the 

 petroleum in question. By means of distillation crude petroleum 

 can be separated into various "fractions," one of the most im- 

 portant of which is gasolene. 



Unfortunately gasolene is not a homogeneous substance, but 

 a complex mixture. Not only do the actual materials constitut- 

 ing it vary, but their relative amounts show wide fluctuations, 

 while still permitting the product to be sold and bought as gaso- 

 lene. These constituent substances are known chemically as 

 hydrocarbons (that is, substances composed of carbon and hydro- 

 gen), and more specifically as paraffin hydrocarbons. 



These constituting members of gasolene have a very close 

 chemical relationship to each other. By way of analog)', they 

 may be compared to a sectional bookcase, in that the latter is 

 composed essentially of a base and one or more units. Just so 

 these parafliin hydrocarbons are composed of their basic sub- 

 stance, added to which, is a varying number of units or incre- 

 ments. Naturally a hydrocarbon composed of the basic substance 

 and, let us say 6 increments, diff^ers in properties from a hydro- 

 carbon composed of the basic substance and 7 increments. Wo 

 can look upon gasolene as a mixture of hydrocarbons, each 

 hydrocarbon being composed of the basic sul)stance and a vary- 

 ing number of increments. 



Since the components of gasolene may show such variation, 

 some specific designation is necessary for the purpose of charac- 

 terization. Unfortunately specific gravity has been chosen for 

 this purpose, as in the early days of the petroleum industry it 

 was soon recognized that the more volatile portions of the crude 

 oil had a lower gravity, in fact that a relationship existed be- 

 tween volatility and gravity. It therefore became customary 

 to sell gasolene on a gravity basis, the Baume gravity scale be- 

 ing generally employed.* That this gravity designation has still 

 survived is very much to be regretted. 



(* According to the Baume scale for liquids lighter than water, the 

 reading increases with decreasing gravity. That is to say, 75-degree Baume 

 corresponds to a lighter gravity than does 60-degree Baume.) 



In the majority of cases it is the volatility of the gasolene 

 which determines its desirability. In order, then, that the desig- 

 nation of the gasolene may be significant, there should be a 

 direct relationship between the gravity and volatility. While 

 this was to a large extent true in the early days of the petroleum 

 industry, when crude oil had only relatively few sources of 

 origin, it no longer holds true to-day. It is a matter of common 

 observation that during recent years the volatility of gasolene 

 has been continually decreasing with little or no change in the 

 gravity. To be sure, in the case of motor gasolene there have 

 been changes in both the volatility and gravity, but the 60-degree 

 gasolene of to-day is much less volatile than the material sold 

 under the same name three or four years ago. 



The more accurate and significant method of designating 

 gasolene is by reference to its boiling points. If gasolene were 

 a homogeneous liquid composed of only one hydrocarbon, it 

 would have a definite boiling point just as water has a definite 

 boiling point of 212 degrees. As has already been pointed out, 

 however, gasolene is not a homogeneous substance but consists 

 of a mixture of closely related hydrocarbons. As these hydro- 

 carbons boil at different temperatures, the mixture obviously 

 cannot show a constant boiling point. It is for this reason that 

 we find that whereas an average sample of gasolene begins to 

 boil around 140 degrees F., a temperature of well over 300 de- 

 grees F. is necessary before all the gasolene will boil. There be- 

 ing a very close relationship between volatility and boiling 

 point, by knowing the temperatures at which definite volumes 

 of gasolene boil, one is in a position to compare accurately the 

 volatility of one gasolene with another. 



For the sake of clarity, there are tabulated below the boiling 

 points of a few samples of gasolene taken at random : 



.4 B C D 



5 per cent boils under. . 194 deg. F. 162 deg. F. 118 deg. F. 145 deg. F. 

 10 per cent boils under.. 197 deg. F. 176 deg. F. 133 deg. F. 147 deg. F. 

 30 per cent boils under.. 212 deg. F. 223 deg. F. 154 deg. F. 165 deg. F. 

 50 per cent boils under.. 221 deg. F. 252 deg. F. 180 deg. F. 192 deg. F. 

 70 per cent boils under.. 244 deg. F. 286 deg. F. 206 deg. F. 221 deg. F, 

 90 per cent boils under. . 289 deg. F. 343 deg. F. 244 deg. F. 302 deg. F. 

 95 per cent boils under.. 314 deg. F. 365 deg. F. 262 deg. F. 329 deg. F. 

 Specific Gravity 61 deg. Be. 60 deg. Be. 71 deg. Be. 72 deg. Be. 



.4 represents a motor gasolene purchased in 1911. 



B represents a motor gasolene of recent date. 



C represents a 71-72-degree Baume gasolene purchased in 1911. 



D represents a 71-72-degree Baume gasolene of recent date. 



Comparing samples A and B, it will be observed that while 

 the gravity of the two gasolenes is practically identical, there is 

 a wide difference in their boiling points. Similar facts are ob- 

 served on comparing samples C and D, which are of practically 

 identical gravity. It is therefore evident that the designation of 

 a gasolene by its gravity gives little indication as to its boiling 

 points, and hence, as to its volatility. It would be much to the 

 benefit of the rubber manufacturer if gasolenes could be bought 

 or even offered on a boiling point basis. It would be sufficient 

 merely to state the temperatures at which say 5, 50 and 95 per 

 cent of the material boils in order to give the purchaser a gen- 

 eral idea regarding its nature. 



The three major uses of gasolene in the rubber industry are 

 in (1) Spreading, (2) Dipped goods, (3) Cements. It may 

 therefore be of interest to refer to the requirements which are 

 demanded of the gasolene in each of these three applications. 



Spreading. B'or spreading purposes it is not desirable to 

 have a gasolene showing extreme boiling points. That is to say, 

 low initial points and liigh final points arc undesirable. On the 

 whole, sample A is a satisfactory gasolene for spreading, but 



